1. Field of the Invention
The present invention relates to an image processing method and a digital camera which use a face extracting technology to improve the picture quality.
2. Description of the Related Art
A related art camera which uses a silver halide film is capable of performing photographing at a low illuminance by using a high-speed film. In recent years, digital cameras featuring a high-speed photography mode which performs photography without using a silver halide film have been developed. This capability is made feasible by a sensitivity enhancement circuit which extends the full-aperture time of the electronic shutter of a solid-state image pick-up device, that is, the storage time of an electric charge on a solid-state image pick-up device, integrates the images of a plurality of frames into a frame memory, or adds peripheral pixels in the same frame.
The photography in the high-speed photography mode experiences an insufficient quantity of light thus includes a noise more often. Such a noise appears as grainness or roughness in an image and degrades the picture quality. In particular, when a noise component is conspicuous on the face of a person as a subject, the most important element of the image, the texture of the skin of the face is impaired, which gives an unfavorable impression to an observer. The region of a human body where the picture quality shows largest degradation due to a noise is the face, which is a site where noise reduction is most effective.
A related art aiming at improvement of the quality of a picture including the face of a subject is disclosed for example in the Japanese Patent Laid-Open No. 2001-309225.
The related art technology disclosed in the Japanese Patent Laid-Open No. 2001-309225 changes the exposure or color balance depending on whether the face of a subject appears in the image. The processing addresses the entire image so that it cannot achieve noise reduction dedicated to the face conducive to improvement of picture quality. For example, performing noise reduction on the entire image removes the edge component of the contour thus resulting in a flat image as a whole.